The present invention concerns cholesteryl-3-hydroxy-bisphosphonic acid derivatives and their soluble salts or hydrates and pharmacologically active conjugates, a method for their manufacture as well as their use for treating diseases.
Phosphonic Acid Derivatives and Their Technical Application
Phosphonic acids are organic components comprising one or several C—PO(OH)2-group(s) with stable covalent carbon-phosphorus bonds. Phosphonates are effective chelating agents for divalent and trivalent metal ions. Most phosphonates are very similar to amino carboxylates such as EDTA, NTA, and DTPA. Moreover, they inhibit very effectively crystal growth and corrosion.
Based on these properties, they are used in numerous technical and industrial applications. An important field of application in industry is their use in cooling water, desalinating systems, and also on oil fields in order to inhibit corrosion. In the textile industry as well as in the paper and pulp production phosphonates are used as stabilizers for bleaching agents in that they act as chelating agents that can deactivated peroxide. An example for environmental use of phosphonates is glyphosate (N-phosphonomethyl glycine), a non-selective herbicide, that controls plant growth by inhibiting a biochemical cascade.
Polyphosphates represent polymers (condensation products) of orthophosphate groups that are bonded by energy-rich phosphoanhydride bonds (oxygen bonding). Polyphosphate (poly-P) is synthesized in the human body and is present almost in all cells. The largest proportion of poly-P can be found in the bone-forming osteoblasts. Poly-P has many functions, depending on which body section is being considered. It stores energy-rich phosphate, complexing calcium or other divalent or cations, it functions as a counter ion for basic amino acids or as a regulator of the intracellular level of adenylate nucleotides.
Poly-P is often used in toothpaste because it is assumed that it prevents caries formation which is assumed to be based on its ability to mineralize hydroxyl apatite and to reduce its acidity as well as its solubility.
The group of bisphosphonates is used for the treatment of different bone diseases and ailments that concern the calcium metabolism.
Bisphosphonates are analogues of pyrophosphate in which oxygen bonding is replaced by a carbon atom with different side chains. The P—C—P group is resistant in regard to enzymatic hydrolysis and for this reason bisphosphonates are not metabolized in the body. Bisphosphonates can be divided into three generations. They differ in regard to the substitution of the hydrogen atom by different side chains at two possible positions in the molecule. Alkyl side chains (for example, etidronate) characterize the first generation. The second generation of bisphosphonate comprises the amino bisphosphonate with a terminal amino group (for example, alendronate). Side chains that have rings are typical of the third generation (for example, zolendronate).
Medical Applications of Phosphonates
In bone scintigraphy phosphonates are used as diagnostic agents. Some differently marked phosphonates, for example, 99mTC-marked phosphonates or 188Re-complexes, are used as radioactive markers in order to make visible in the skeleton the presence, the location, and the degree of diseases, such as osteomyelitis, bone neoplasms, arthritis or bone infarcts.
The most important pharmacological effect of bisphosphonate is the inhibition of bone resorption. They have, like pyrophosphate, a high affinity to hydroxyl apatite, the main component of the bone, and prevent its growth as well as its decomposition. Moreover, they deactivate osteoclastic cells, called osteoclasts, in that they cause their apoptosis. Normally, the osteoclasts cooperate with bone-forming cells, the osteoblasts, in order to rebuild the existing bone. They target bone areas that have a high osteoclast activity and they contribute to the regeneration of the normal conditions between osteoblast activity and osteoclast activity.
Bisphosphonates are used in the therapy of bone diseases, usually in the case of Paget disease, hypercalcaemia, osteoporosis and neoplasms.
A further advantage of this group is that they can effect apoptosis of tumor cells. Therefore, they play an important role in cancer therapy (for example, in the case of breast cancer, metastases caused by prostate cancer, or in the case of multiple myeloma).
Derivatives that are comprised of acyclic nucleosidic phosphonates (for example, cidofovir or tenofovir) are effective against a large number of diseases caused by DNA viruses and retroviruses. Acyclic nucleosidic phosphonates (ANPs) are analogues in which one phosphonate is bonded by means of an aliphatic chain via an ether bond to a purine or a pyrimidine. As soon as these analogues are phosphorylized in the cell, they compete with naturally occurring nucleotides in nucleic acid synthesis; as a result of this, the virus replication in the infected cells is reduced or prevented.
The antiviral activity of ANPs is also utilized in veterinary medicine. They are potent inhibitors of the feline immunodeficiency virus (FIV). FIV is similar to the HI virus with regard to morphological, physical, and biochemical properties.
Homing Application for Effective Ingredients/Homing Ligands
As a result of the extraordinary affinity of bisphosphonates to hydroxyl apatite their suitability for homing applications in connection with pharmacologically active substances on the bone was examined. An example for this is the bonding of bisphosphonate, having a high affinity to bone, and growth factors (for example, bovin e serum albumin) that have the ability to stimulate bone growth. Radioisotopes, anti-neoplastic agents, and anti-inflammatory substances have also been bonded to these homing ligands.
The expression “active ingredient homing application” comprises substances that enable a time-controlled release, an organ-specific application, protection, extended in-vivo action, and reduction of toxicity of the active ingredients. Many carrier systems, for example, polymers, nanoparticles, microspheres, micelles, protein carrier systems, DNA complexes as well as liposomes have been used in order to extend the circulation time of different molecules in order to carry them to the desired location of action and in order to protect them from decomposition within the plasma. Liposomes have been utilized in the past as active ingredient carriers in various applications. They have colloidal, vesicular structures on the bases of (phosphor)-lipid bilayer membranes. Because of these structural properties they can encapsulate hydrophilic as well as hydrophobic molecules. Moreover, liposomes can be biologically decomposed and are essentially non-poisonous because they are comprised of natural biomolecules.
A limiting factor of liposomes as an active ingredient carrier is their decomposition by macrophages (copper cells) in the liver and in the spleen directly after intravenous application. The speed and the degree of their uptake are dependent on the rigidity of the membrane, the liposome size, and the dosage. A modification of the liposome surface can reduce the undesirable decomposition by macrophages. By bonding PEG units to the external membrane the circulation time can be increased significantly (long-circulating liposomes). Alternatively, homing molecules can be attached to the liposome bilayers in order to make these structures specific for the location of action, for example, immuno liposomes (liposomes that have at their surface covalently bonded antibodies as homing ligands); they can also be provided with long-circulating properties.
Passive Homing Application
Long-circulating liposomes have the tendency to accumulate in tissues that have a permeable endothelium. These “passive properties of the homing application” are very useful for the homing application on tumor tissues because the arrangement of the blood vessels of most tumors is sufficiently permeable for liposomes. Moreover, because the lymphatic tissue in tumors is usually not fully developed, the extrava sated liposomes have the tendency to remain within the interstitial spaces of the tumor tissue.
Long-circulating liposomes are used frequently as carriers for therapeutic cancer agents, for example, doxorubicin, cisplatinum, vincristine, and camphotecin.
Cholesterol
Cholesterol, when looking at its structure, is an important component of cell membranes. It has an effect on the physical properties of the membrane, especially its fluidity. It is used very frequently in the pharmaceutical industry, in particular, as a component of liposomes. Cholesterol has the property to make membranes more stiff. The addition of cholesterol transforms the membrane into an ordered fluid state across a wide temperature range. Moreover, the use of newly synthesized cholesterol derivatives has been studied already early on.
The afore described components have a plurality of positive properties in the treatment of the aforementioned diseases as well as in the administration of active ingredients.